This invention in general relates to photography and in particular to a photographic camera having either a built-in or detachably connectable electronic flash having a preferred angular distribution in the intensity of its illumination.
2. Description of the Prior Art
Electronic flash units for providing artificial illumination during photographic exposures to supplement natural light of low intensity are well-known in the art. Such electronic flash units are generally adapted to receive an external, substantially steady state DC battery voltage which powers a voltage converter in a conventional manner to convert the DC voltage, which may be on the order of 6 volts, to a suitable flash operating voltage. A charging current from the voltage converter is directed to a storage capacitor so as to gradually charge the storage capacitor to a DC voltage level which may be on the order of 350 volts. The charge stored in the capacitor is discharged by some suitable means through a tube which is filled with a mixture of rare gases such as argon, krypton or xenon. Through the well-known process of vapor discharge, the energy stored in the capacitor dissipated in this manner produces a brilliant flash of light for illuminating the scene.
The brilliance of the flash depends on the type of tube and the quantity of electrically discharged through it from the capacitor. The output of the tube is measured in watt-seconds or joules and depends on how efficiently the electrical charge stored in the capacitor is converted to radiant energy.
The radiant energy emanating from the tube travels in directions away from the tube which depend on the geometry of the tube. Some of this light naturally falls on the subject while as much or more travels away from the subject and is wasted. To optimize the amount of light falling on the scene, it is the usual practice to provide a selectively shaped reflector for intercepting rays of light traveling away from the subject and directing such rays toward the scene. It is usual to selectively shape such reflectors so that the distribution of the intensity of the illumination falling on the scene is uniform thereover.
Recently, compact versions of such electronic flash units have been adapted for use with self-developing type cameras which utilize film cassettes having a battery therein to provide power for various camera systems. In operation, such electronic flash units are connected to a camera which is loaded with a battery carrying cassette. The camera thereafter provides the electronic flash unit with a steady state input voltage which is utilized by the electronic flash unit to charge its storage capacitor. The storage capacitor is thereafter triggered at an appropriate time during the camera exposure interval by a select trigger signal furnished by the camera to discharge the capacitor through the flash tube thereby providing a source of artificial illumination. Such an electronic flash is described, for example, in U.S. Pat. No. 4,074,295 issued to Richard C. Kee on Feb. 14, 1978 and entitled "Compact Accessory Strobe For Cameras With Battery Enclosed Film Pack" and in U.S. Pat. No. 4,085,414 issued to John P. Burgarella on Apr. 18, 1978 and entitled "Electronic Flash Apparatus With Extendable On/Off Switch Control Apparatus".
In the virtually automatic self-developing type camera that is adapted to utilize an electronic flash and supply the power to charge the capacitor thereof from a battery contained in the film cassette positioned within the camera, it is obviously desirable that the electronic flash unit utilize as little of the battery energy as possible and also to convert that energy in an efficient manner to radiant energy since there are a number of camera electrical systems competing for the power contained in the film cassette battery. Those skilled in the art of designing automatic self-developing type cameras which utilize a single battery of limited capacity to power an entire camera cycle are sensitive to the demands which are placed on such a battery and have designed electronic control apparatus by which different camera electrical systems are automatically scheduled to derive power from the battery at different times in order to minimize current drain and in order to get maximum utility from the battery. For example, U.S. Pat. No. 3,846,812 discloses equipment which operates a flash camera of the automatic self-developing type so that only one operation of significant current drain occurs at a time. A film transport motor and a flash unit of the camera accordingly draw battery current at different times.
With the advent of automatic focusing arrangements for use in the self-developing type cameras, additional electrical operating loads of relatively high current drain are imposed on the camera battery. When such operations overlap with other camera operations of significant current drain, the battery voltage is likely to drop to such a degree that the battery is incapable of properly operating the camera. To overcome the additional current drains imposed by automatic focusing systems which are incorporated in self-developing type cameras those skilled in the art have provided camera control systems by which high current operations such as electronic flash unit charging are scheduled to occur one at a time so that a single battery can effectively power all the camera operations. Such a system is described, for example, in U.S. Pat. No. 4,156,565 issued to George C. Harrison on May 29, 1979 and entitled "Control System For Flash-Illuminated Automatic Focusing Camera".
It is evident in view of the prior art discussed above that electronic flash systems which are utilized in self-developing type cameras of the sort described should make maximum use for scene illumination purposes of whatever power is available as scheduled by the control circuit of the camera. For this purpose it has been the practice in the past to provide reflectors for increasing the illumination which falls on a photographic scene in order to make the most efficient use of the radiant energy available from a flash unit tube. Such reflectors have traditionally been shaped to redirect the illumination from the flash unit tube in such a way that the radiant energy from the flash tube, which includes the direct illumination from the tube as well as that reflected off of the reflector, is distributed so that the intensity thereof is symmetrically disposed about the camera optical axis and is also as uniform as possible.
It is a primary object of the present invention to provide an electronic flash unit which can be either built into a photographic camera or detachably connected thereto to provide a preferred distribution of illumination which permits maximum use of power available to the flash unit such that the maximum flash range of the camera which utilizes the electronic flash unit is greater than it would be with a flash unit having a uniformly distributed illumination pattern operating at similar available power.
Other objects of the ivention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the constuction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure.